The invention relates to an optical storage apparatus using a rewritable medium such as an MO cartridge or the like and, more particularly, to an optical storage apparatus for efficiently adjusting a light emitting power of a laser diode to an optimum power at the time of loading of a medium.
Attention is paid to an optical disk as a memory medium which is a main medium of multimedia that is rapidly developing in recent years. For example, in MO cartridges of 3.5 inches, in addition to the conventional MO cartridges of 128 MB and 230 MB, media of a high density recording of 540 MB and 640 MB are also being provided in recent years. Therefore, as an optical disk drive, it is desirable that the optical disk drive can use all of the media of 180 MB, 230 MB, 540 MB, and 640 MB which are available at present. In personal computers which have rapidly been spread in recent years, a reproducing function of a compact disc (CD) known as a read only medium is indispensable. It is difficult to install an optical disk drive for an MO cartridge as a rewritable optical disk apparatus in addition to an optical disk drive for a CD from viewpoints of the space and costs. In recent years, therefore, an optical disk drive which can use both of an MO cartridge and a CD has also been developed. In such an optical disk drive of the CD/MO common-use type, with respect to an optical system, a mechanical structure, and a controller circuit unit, they are commonly used for both of the CD and MO cartridge as much as possible.
In the MO cartridge that is used in the optical disk drive, on the other hand, a medium track is divided into zones and a ZCAV recording (zone constant angular velocity recording) in which the numbers of sectors of the zones are equalized is used. The number of zones of the MO medium is set to one zone in the conventional 128 MB medium and to ten zones in the 230 MB medium. On the other hand, in a high density PWM recording medium of 540 MB or 640 MB which has been put into practical use in recent years, in association with the improvement of a recording density, a track pitch of the medium is narrowed and the number of zones is also increased. Namely, although the number of zones in the 640 MB medium is set to 11 zones and the number of zones in the 540 MB medium is set to 18 zones. Ordinarily, in case of the optical disk medium using the MO cartridge, since there is a difference in the light emitting power (namely, the recording power of a laser diode for the optimum recording every medium), when the medium is loaded, a test write is executed in every zone and a light emission adjustment to adjust to the optimum recording power is executed. In the conventional 128 MB or 230 MB medium, the recording is performed by a pit position modulation (PPM) and it is sufficient that the light emitting power of the laser diode is changed to two levels of an erasing power and a recording power. On the other hand, in the PWM recording medium of 540 MB or 640 MB, a recording by a pulse train is used to raise a recording density. In the pulse train recording, it is necessary to change the light emitting power of the laser diode to three levels of an erasing power, a first writing power, and a second writing power. Therefore, with respect to the medium of 540 MB or 640 MB in which the number of zones is increased, if the light emission adjustment of the laser diode is performed in every zone, there is a problem such that in addition to an increase in the number of kinds of light emitting powers due to the pulse train recording, it takes a long time for adjustment. At the time of the adjustment of the light emission of the laser diode, as compared with an instantaneous light emission in the actual PPM recording or PWM recording, the light emission is driven by a default value that is designated by firmware for a relatively long time during which the adjustment is necessary. This substantially results in that the laser diode is DC light emitted (continuous light emission). If the light emission adjustment is performed by a high light emitting power, damage may occur to the laser diode and there is a fear such that deterioration is hastened.
In the conventional optical disk drive, as a writing power which is used to write data onto a medium, an optimum power differs depending on the kind and temperature of the medium. Therefore, when the medium is loaded to the optical disk drive, a power adjusting process of the laser diode for deciding the optimum power is executed by performing a test write of a test pattern, namely, a test write to the medium. According to a conventional power adjusting process of the laser diode, as shown in FIG. 1, the writing power given as a default power is set to a power at a start point 401 and, for example, the writing and reading operations of a test pattern are repeated while decreasing the writing power step by step, thereby counting the number of times of dissidence of the data (the number of errors). When the writing power is reduced to a value near a limit power, the number of times of dissidence of data increases. For example, a limit power WPa at a limit point 404 exceeding 1000 data dissidence times is obtained. Subsequently, the writing and reading operations of the test pattern are repeated while increasing the writing power step by step from the start point 401, thereby counting the number of times of dissidence of data (the number of errors). When the writing power is increased to a value near a limit power, the number of times of dissidence of data increases. For example, a limit power WPb at a limit point 406 exceeding 1000 data dissidence times is obtained. When the upper and lower limit powers WPa and WPb can be detected as mentioned above, the intermediate writing power (WPb-WPa)/2 is determined as an optimum writing power WP-best. However, in the adjusting process of the writing power of the laser diode in association with the test write in such a conventional optical disk drive, two limit powers have to be detected while increasing and decreasing the writing power by setting a starting power to an initial point. Therefore, it takes time to detect the limit powers and, there is a problem such that, it takes time, for example, until the apparatus enters a ready state after the medium has been loaded. On the other hand, since it is necessary to perform the test write by driving the laser diode by a high power for the writing power adjustment, a large burden is exerted on the laser diode. Moreover, since the writing power adjustment is also frequently performed during the use of the apparatus, there are problems such that the deterioration of the laser diode is hastened and a durability of the apparatus is lost.